Medicament and apparatus for treating chronic kidney disease

ABSTRACT

The present invention provides a novel therapy concept based on a removal of circulation BSP (bone sialoprotein) from the plasma of patients with chronic kidney disease (CKD), preferably by plasmapheresis or an administration of antibodies against BSP in plasma. The present invention further provides a BSP absorber material for plasmapheresis and a pharmaceutical composition namely in form of anti-BSP antibodies for direct administration which are biocompatible in humans. The beneficial effects of this therapy have been proven by the observed correspondence between levels of circulating free BSP levels and mortality of CKD patients.

FIELD OF THE INVENTION

The present invention relates to a medicament, apparatus and method for treating chronic kidney disease.

BACKGROUND OF THE INVENTION

Chronic kidney disease (CKD), also known as chronic renal disease (CRD) affects about 10% of the population in Europe and North America. CKD is characterized by a progressive loss in renal function over a period of months or years. The Kidney Disease Improving Global Outcomes (KDIGO) statement has defined CKD as either kidney damage or reduced glomerular filtration rate (GFR) to less than 60 mL/min/1.73 m2 sustained for more than 3 months (cf. KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD, Kidney Int 76; Suppl. 113, 2009). There is no specific treatment unequivocally shown to slow the worsening of CDK except for cases where there is a specific underlying cause to CKD such as vasculitis. A permanent kidney failure then requires a renal replacement therapy which may be a form of dialysis or a kidney transplant. As CKD progresses and GFR declines, mineral metabolism disturbances increase and hyperphosphatemia occurs along with a reduction in renal 1a-hydroxylation of 25-hydroxyvitamin D and low circulating levels of calcitriol which in turn cause a decrease of intestinal calcium absorption. The disturbed calcium and phosphate homeostasis causes variable degrees of hypocalcemia and secondary hyperparathyroidism, with concomitant abnormalities in bone turnover and metabolic bone disease. The mineral and bone disorder (MBD) is a common manifestation of CKD. Other symptoms of CKD include increase blood pressure, iron deficiency anaemia, metabolic acidosis, azotemia and uraemia, an activation of the sympathetic tone, inflammation and oxidative stress. CDK goes therefore in line with high morbidity and mortality. CKD patients suffer in particular from accelerated atherosclerosis and tissue calcification. CKD patients on dialysis or with end stage renal disease (ESRD) are more likely to die from cardiovascular complications than from kidney failure (Kettler M et al, Nephrology 2009, 14: 389-394).

The progress of arterial and vascular calcification is linked to a dysregulated mineral metabolism and altered levels of serum calcium and calcium-phosphorus products. The elevated extracellular levels of these minerals further affect the survival and phenotype of vascular smooth muscle cells and myocardial cells. The calcification, mostly as calcium hydroxyl apatite deposits, may occur in blood vessels, the myocardium and cardiac valves. In the arterial vessel wall, calcification takes place in the intima or In the media. Medial calcification (also referred to as Monckeberg sclerosis) is the form classically associated with age, diabetes and CKD.

Conventional therapeutic approaches are usually directed to bringing the biochemical parameters to ranges associated with lower mortality. They comprise (a) a use of an adapted dialysate calcium concentration; (b) a use of phosphate-binding agents; (c) the administration of calcitriol or vitamin D analogues; (d) the use of calcimimetics; (d) diet recommendations (reducing dietary phosphate intake and administering phosphate binders and calcium supplements); and/or (e) the uptake of native vitamin D supplements. WO 2011/000086 A1 (University of Alberta) discloses an method and apparatus for reducing serum phosphate levels and calcium product in patients by hemodialysis since observational data suggest that higher doses of calcium-based phosphate binders may contribute to vascular calcification. There is generally a considerable interest in controlling serum phosphate while minimizing oral calcium load. On the other hand, most phosphate is intracellular and thus unavailable to hemodialysis. WO 2011/130528 A (Fresenius Medical Care Holdings Inc., US) discloses an extracorporeal blood treatment system including a calcium trap wherein an immobilized species is adapted to reduce the calcium concentration in the blood to a concentration that prevents blood clotting thereby producing calcium-depleted blood. However, there are no specific drugs or intervention methods available for interfering with the pathogenesis of vascular and tissue calcification. There is also a need for more drugs and intervention methods against the cardiovascular risks concomitant CKD, ESRD and renal replacement therapies. The prior art therefore represents a problem.

SUMMARY OF THE INVENTION

The object of the invention is achieved by medicament for treating extracellular tissue and vascular calcification, atherosclerosis, arteriosclerosis, and arterial calcification and the cardiovascular risks concomitant CKD, ESRD and renal replacement therapies comprising an effective amount of a receptor molecule recognizing human bone-sialoprotein (BSP) in blood, plasma or serum. The medicament may be a human monoclonal antibody or a humanized monoclonal antibody or a rat monoclonal antibody. The medicament may preferably be an antibody which comprises one or more functional portions of a protein sequence as disclosed in any of SEQ ID NOS: 1, 2, 3, 4, 5, and 6. Functional or essential portion means in this connection portion of the molecular which take part in the detection and binding of human BSP in plasma. Not comprised are therefore linker portions, leader sequences which are cut off during protein maturation, or interchangeable portions of the antibody. An essential portion of the receptor molecule or antibody therefore relates to the one or more of complement determining regions (CDR) contained in any of the sequences with SED ID NO: 1, 2, 3, 4, 5, and 6, as those are required for recognition and binding of human BSP in plasma or serum. Conservative protein substitutions and insertions are known to those skilled in the art.

The invention further comprises a medicament for treating extracellular tissue and vascular calcification wherein the receptor molecule recognizes an antigen determinant or epitope of BSP which is accessible in plasma and bound by an antibody having any protein sequence of SEQ ID NO: 1, 2, 3, 4, 5, and 6. The term tissue and vascular calcification shall encompass the cardiovascular risks concomitant CKD, ESRD and renal replacement therapy and also comprise the terms arteriosclerosis and atherosclerosis. While CKD is generally associated with increased risk of coronary heart disease the knowledge with respect to the histopathologic characteristics of coronary atherosclerosis in individuals with CKD is scarce and the terms arteriosclerosis and atherosclerosis, while intrinsically relating to different etiologies, often used interchangeably. However, the frequencies of advanced atherosclerotic lesion due to arterial calcifications is increasing with a concomitant decrease of the GTR. On the other hand, there is also a strong link between total cholesterol, calcium-phosphorus product, diabetes, hypertension, serum creatinine and cardio-vascular risks.

Another embodiment of the invention further relates to a receptor molecule or antibody as described which is bound to or contained in any solid phase material selected from beads, agarose, material used for apheresis, material used for plasmapheresis, microliter plate, vessel wall. The receptor molecule or antibody of any may be comprised in a diagnostic system or kit, preferably a kit for companion diagnostic of renal replacement therapy, dialysis, CKD, ESRD, tissue and vascular calcification, atherosclerosis, arteriosclerosis, arterial calcification. The companion diagnostic may in particular also relate to an evaluation of the risks for arteriosclerotic lesions in individuals with CKD or ESRD, and for an evaluation of the cardiovascular risks in general.

Another aspect of the invention relates to an extracorporeal blood treatment system comprising means for withdrawing blood from a patient; means for separating blood cells and plasma; means for transporting the plasma through a trap for soluble BSP, the BSP trap including a substrate having an immobilized species, the species being adapted to reduce the soluble BSP concentration in the blood to a concentration that prevents vascular and tissue calcification, thereby producing BSP-depleted plasma; and means for returning treated plasma and blood cells back to the patient. In a preferred embodiment the extracorporeal blood treatment system may further comprise means for transporting the blood and/or plasma through a calcium trap, the calcium trap including a substrate having an immobilized species, the species being adapted to reduce the calcium concentration in the blood to a concentration that prevents formation of a precipitate of calcium and BSP in the extracorporeal blood treatment system, thereby producing calcium-depleted blood; means for treating the calcium-depleted blood or plasma downstream of the calcium trap by an extracorporeal plasma treatment device, which may also comprise a trap for bone sialoprotein; and means for infusing calcium into the treated calcium-depleted blood downstream of the extracorporeal blood treatment device to add calcium to the treated calcium-depleted blood. Thus, another aspect disclosed herein relates to a method for plasmapheresis comprising the use of a trap for soluble BSP.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is best understood when read in conjunction with the accompanying figures, which serve to illustrate the preferred embodiments. It is understood, however, that the invention is not limited to the specific embodiments disclosed in the figures.

FIG. 1 is a diagram of the body weights of rats subjected to sham surgery (healthy), 5/6 Nx nephrectomy 5 (uremic calcification) and 5/6 Nx as well as anti-BSP-IDK1 mAb therapy during five weeks of uremic calcification diet (high phosphate, calcium and calcitriol) as described in example 2;

FIG. 2 is a column diagram summarizing the effect of the anti-BSP mAb therapy on basis of the media to lumen ratio (intrarenal arteries) and of renal perivascular fibrosis, again for rats subjected to sham surgery, 5/6 Nx and placebo treatment and 5/6 Nx and anti-BSP IDK1 mAb therapy after five weeks of uremic calcification diet as described;

FIG. 3 is a column diagram summarizing the effect of an anti-BSP IDK1 mAb treatment on plasma levels of cystatin-C for healthy and renally impaired rats as described in example 2;

FIG. 4 is a column diagram summarizing the effects of an anti-BSP IDK1 mAb treatment on the glomerulosclerosis index;

FIG. 5 is a column diagram summarizing the effect of an anti-BSP IDK1 mAb treatment on renal collagen Ill;

FIG. 6 is a column diagram summarizing the effect of an anti-BSP IDK1 mAb treatment on cardiac interstitial fibrosis;

FIG. 7 is a column diagram summarizing the effect of an anti-BSP IDK1 mAb treatment on cardiac perivascular fibrosis;

FIG. 8 is a column diagram summarizing the effect of the anti-BSP IDK1 mAb therapy on the calcification of the aorta;

FIG. 9 is a column diagram summarizing the effect of the anti-BSB IDK1 mAb therapy of RT aorta-MMP9;

FIG. 10 is a diagram on the binding kinetics of BSP to an anti-BSP mAb agarose;

FIG. 11 is a diagram on the effect of temperature on the binding kinetics of BSP to an anti-BSP IDK mAb agarose;

FIG. 12 is a diagram on the numbers of apheresis on the binding kinetics of BSP to an anti-BSP IDK mAb agarose.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel therapy concept based on a removal of circulation BSP (bone sialoprotein) from the plasma of patients with chronic kidney disease (CKD), preferably by plasmapheresis or an administration of antibodies against BSP in plasma. The present invention further provides a BSP absorber material for plasmapheresis and a pharmaceutical composition for direct administration which are biocompatible in humans. The beneficial effects of this therapy have been proven by the observed correspondence between levels of circulating free BSP levels and mortality of CKD patients.

The mechanism of arterial calcification is complex, but without wishing to be bound by any theory, the first step appears to be a de-differentiation or transformation of vascular smooth muscle cells (VSMC) into an osteoblast/chondrocytic phenotype. VSMCs originate from a similar mesenchymal stem cell as osteoblasts. It is believed that transcription factor core binding factor al (Cbfa-1; encoded by the RUNX2 gene) is responsible for the phenotypic transformation of VSMCs to osteoblast cells. The signals that induce a transformation to an osteoblast/chondrocytic phenotype, however, are multiple. In both bone and arteries, there are inhibitors of calcification, including matrix gla proteins, pyrophosphate, and osteopontin, and circulating inhibitors such as fetuin-A. Calcification occurs if there is an imbalance between inhibitors of calcification and pro-mineralizing factors that stimulate VSMC de-differentiation.

Bone sialoprotein (BSP), a phosphorylated glycoprotein, is an important component of extracellular matrix. BSP is usually expressed by cells which take part in the formation of dentin, bones and cartilage but it also an adhesion molecule which can bring about attachment of cells on the tissue matrix. BSP binds to the integrin receptors through its recognition sequence (arginine-glycine-aspartate, RGD). BSP forms in vitro crystallization nuclei for biological apatite and in vivo it takes part in mineralization. The switching off of the BSP gene in knock-out mice leads however to no recognizable disruption of the building and functioning of the skeleton. On the other hand, BSP is involved in tissue calcification as its binding to collagen is needed to initiate bone mineralization and the adhesion of osteoblasts to the mineralized matrix (Ogata Y, J. Periodontal Res. 2008, 43(2): 127-135). WO 00/36919 discloses a suppression of the expression of BSP in tumor and connective tissue cells which promote calcification. In vitro studies suggest that BSP is involved in the transformation from VSMC to osteoblast-like cells and that a pharmacologically reduced expression of BSP may lead to a deceleration of this transformation process. By immune-histochemical methods we also discovered BSP in the core of aortal calcifications from uremic, calcitriol treated rats (Haffner D et al, J Hypertens 2005, 23(5): 1067-76), Cell culture experiments with VSMC suggest that calcitriol causes an up-regulation of pro-mineralizing genes, including BSP (Zebger-Gong H et al, J Hypertens. 2011, 29(2):339-48).

While BSP plays an important role in bone turnover literature suggests that an elimination of circulating BSP poses no risk regarding bone health. BSP knockout mice only show a reduction in bone turnover, with a reduced recruitment of osteoclasts. Mice over-expressing BSP have an elevated bone turnover as evidenced by elevated calcium and reduced PTH levels. There is however no clinical or other evidence that an elimination of BSP from plasma may cause osteoporosis. Postmenopausal woman suffering from osteoporosis show elevated levels of serum BSP compared to perimenopausal healthy controls. Treatment with alendronic Acid® (INN) as well as hormone replacement therapy, both established treatment options of osteoporosis, lead to a reduction of serum BSP levels in postmenopausal women.

Calcified lesions contain osteoblasts, osteoclasts, trabeculae and numerous proteins regulating calcification such as osteopontin, alkaline phosphatase and bone sialoprotein. More precisely, we have discovered an immunostaining for BSP and other pro-mineralizing proteins regulating calcification prior overt calcification in the arteries of ESRD patients. This has lead us to the assumption that a deposition of BSP precedes calcification so that it could be target for specific inhibition of tissue and arterial calcification. As BSP has such a central role in the calcification progress we initiated experiments on whether vascular and soft tissue calcification is reduced and the overall outcome of renally impaired patients with CKD or ESRD is improved by interfering with this protein using therapeutic antibodies. Alternatively, BSP may be removed from circulation using plasmapheresis. Our new therapeutic approach aims at reducing uremic vascular and soft tissue calcification and improving overall outcome of CKD by modulating the concentrations of circulating BSP in plasma. This may be achieved by the development of a plasmapheresis intervention that eliminates excess BSP from the circulation in a hemodialysis process.

Initial experiments conducted in uremic rats subjected to a 5/6 nephrectomy (5/6Nx) indicate that the administration of an anti-BSP-antibody goes in line with decreased calcification, decreased media-to-lumen ratio of intrarenal vessels and decreased perivascular fibrosis of intrarenal vessels. Thus, we have adapted the novel therapy concept to a medical device using plasmapheresis to remove BSP from patients.

EXAMPLES Example 1—Method of Inducing Vascular and Tissue Calcification in Rats

Among the available experimental models, the 5/6 nephrectomy (5/6 Nx) of rats is most used for studies of progressive renal disease. This is because the features of this experimental procedure are common to CKD observed in humans [Kren S et al, The course of the remnant kidney model in mice. Kidney int. 1999; 56:333-337]. The 5/6 nephrectomy has also been established to test new therapies and has been proven to be clinically relevant [Fujihara C K et al, Losartan-hydrochlorothiazide association promotes lasting blood pressure normalization and completely arrests long-term renal injury in the 5/6 ablation model. Am J Physiol Renal Physiol. 2007; 292:F1810-1818; Terzi F et al, Sodium restriction decreases AP-1 activation after nephron reduction in the rat: role in the progression of renal lesions. Exp Nephrol. 2000; 8:104-114; Waanders F et al, Effect of renin-angiotensin-aldosterone system inhibition, dietary sodium restriction, and/or diuretics on urinary kidney injury molecule 1 excretion in nondiabetic proteinuric kidney disease: a post hoc analysis of a randomized controlled trial. Am J Kidney Dis. 2009; 53:16-25]. The 5/6 nephrectomy can be performed by unilateral nephrectomy and either partial infarction or amputation of the poles of the remaining kidney [Santos L S et al, Surgical reduction of the renal mass in rats: morphologic and functional analysis on the remnant kidney. Acta Cir Bras. 2006; 21:252-257].

Male Wistar rats weighing about 100 g were used for all experiments. They were subjected to a 5/6 nephrectomy by two surgeries within two weeks. One week after the first surgery, the kidney remnant rats were further fed a diet comprising 1.2% phosphate and 0.9% calcium to induce tissue and vascular calcification. One week after the second surgery the animals further received oral doses of calcitriol of 0.25 mg/kg which suppresses parathyroid hormone production. The calcitriol administration further promotes vascular calcifications by several mechanisms: (i) an increase in intestinal calcium and phosphate absorption; (ii) over suppression of parathyroid hormone resulting in low bone turnover disease and diminished calcium delivery to the bone; and (iii) direct effects on the vascular wall. Thus, we specifically examined in the instant animal experiment the calcification of arterial vessels of sham and remnant kidney rats (Wistar) subjected to a phosphate and calcium enriched diet and additional doses of active vitamin D. The therapy of the invention was tested by treating the kidney remnant rats by a subcutaneous administration of various doses of a rat IgG monoclonal antibody specific for circulating soluble bone sialoprotein (BSP). No hypersensitivity or adverse side reactions of the mAb therapy against soluble BSP were observed, in particular no allergic reactions or inflammations. The systemic response was good and no side effects observed. No changes in blood pressures were observed between healthy and nephrectomized rats during the text period.

Results were obtained for rats subjected to sham surgery and diet only (n=10), 5/6 Nx rats receiving placebo (n=14), and 5/6 Nx rats receiving a therapy with 5 monoclonal rat antibody specific for circulating soluble bone sialoprotein (anti-BSP-mAb): low dose therapy (n=14; 3 mg mAb/kg/week); medium dose (n=14; 10 mg mAb/kg/week) and high dose (n=14; 30 mg/kg/week). The uremic control was represented by 5/6 Nx rats (n=10) receiving a high phosphate and calcium diet but no calcitriol. Aortic medial calcification can be reduced vis-ci-vis untreated controls by a 10 systemic treatment with the matrix metalloproteinase inhibitor such as doxycycline (Qin X et al, Matrix metalloproteinase inhibition attenuates aortic calcification. Arterioscler Thromb Vase Biol 2006; 26: 1510-1516). Thus, a further control group consisted of 5/6Nx rats (n=14) receiving a phosphorous calcium diet as well as doses of doxycycline (n=14); control (n=6).

The rat blood pressures were measured non-Invasively first time three days after the first treatment with anti-BSP mAb by determining the tail blood volume with a sensor and an occlusion tail cuff. The treatments by anti-BSP mAbs were repeated in weakly intervals using low, medium, and high doses, respectively. Five weeks after the first treatment by anti-BSP mAbs, tail blood was taken and the animals 20 killed by a use of isoflurane gas. The organs (kidney, heart, aorta) were taken for further histological analyses: von Kossa staining for quantifying mineralization and calcification in tissue sections; Sirius Red staining (connective tissue staining) for quantifying interstitial and perivascular fibrosis; Elastica van Gieson staining (connective tissue staining solution) for determining the media to lumen ratio in cardiac 25 and renal vessels; PAS diastase staining for determining glomerulosclerosis; by wet chemistry for the presence of calcium and phosphate products; by Western blotting for collagen I, collagen II, TGF-β1, SMAD-2, CTGF; and by RT-PCR for TRPS, P21, VDR, MMP2, MMP9, osteopontin, ANP, TRPV6, calbindin, BSP, CBFA1, osterix, osteocalcin. Measured blood plasma parameters: creatinine, calcium, phosphate, magnesium, fetuin A, FGF-23, beta2-microglobulin; calbindin, clusterin, cystatin-C, NGAL, osteopontin, TIMP-1, VEGF.

Example 2—Results of the Anti-BSP mAb Therapy in Rats

Visual Inspection of Aorta and Remnant Kidney

The organs were taken at end and visually inspected. The aortas from healthy (sham) animals showed no signs of aortic calcification, no atherosclerotic intima lesions and no ‘artheriosclerotic’ intima/media lesions. The aortas from 5/6 Nx kidney remnant rats, which had received a phosphorus calcium diet and calcitriol, showed massive aortic calcifications and dilated aorta brackets. The thoracic and abdominal regions of the aortas of the Nx rats further showed dilated calcified brackets. Whereas healthy (sham) animals showed no symptoms for a kidney disease, the remnant kidneys of the 5/6 Nx rats were edematous enlarged and whitely colored as typical for uremic calcification.

Body Weight

The body weight of healthy (sham) and 5/6 Nx rats were significantly different after five weeks. The body weights of the healthy animals increased gradually during the five weeks period whereas the body weights of placebo-treated 5/6 Nx rats increased at the beginning and decreased with progressing calcification treatment. On the other hand, the body weights of anti-BSP mAb treated 5/6 Nx rats increased during the entire period of five weeks so that the body weights of anti-BSP-mAb treated animals were significantly higher than for untreated animals. These results have been summarized in FIG. 1. Thus, 5/6 Nx rats which had undergone an anti-BSP-mAb therapy had significantly higher body weights compared to controls after 5 weeks (*p<0.05 mAb-BSP therapy pooled compared with 5/6 Nx controls).

Mortality

The mortality of placebo-treated 5/6 Nx rats (4 out of 14 after four weeks) was significantly higher compared to rats which had received a low, medium, or high dose anti-BSP mAb treatment (2/14 and 4/14 and 2/14) or sham (0/10) only.

Cystatin C and Kidney Function

The plasma level of cystatin C is a parameter reflecting the glomerular filtration rate (GFR) and kidney function. FIG. 2 is a column diagram comparing the plasma cystatin C levels for 5/6 Nx rats which had received an anti-BSP-mAb therapy (pooled for low, medium and high dose therapy) and 5/6 Nx rats which received a treatment with a placebo. The Mann-Whitney U test (MWU) of the data supports significantly lower cystatin C values for 5/6Nx animals (pooled) which had received an anti-BSP mAb therapy compared to untreated 5/6 Nx controls (***p<0.0001).

Histological Examination of Kidneys

The kidney were histologically examined after staining. No large differences could be detected after the von Kossa staining for calcium products. The Sirius Red staining showed a trend to reduced interstitial fibrosis, and the PAS staining a significantly reduced glomerulosclerosis (see FIG. 4) and media to lumen ratio (FIG. 3 A/B) for 5/6 Nx rats which had received an anti-BSP therapy. More precisely, 5/6 Nx rats subjected to an anti-BSP mAb therapy had significantly less glomerulosclerosis compared to untreated 5/6 Nx controls (***p<0.0001; *p<0.05); anti-BSP treated 5/6 Nx rats also showed a significantly reduced media to lumen ratio compared to untreated controls at intrarenal vessels as well as a reduced perivascular fibrosis.

Analysis for Matrix Proteins and Expression of Vitamin D Receptor.

5/6 Nx rat subjected to an anti-BSP mAb therapy showed a trend to a lowered expression of the matrix protein collagen I and collagen III (FIG. 5) when analyzed by Western blot analysis, compared to placebo treated rats and sham. The standard deviation of the results however was high so that the result is only significant for collagen III. The RT-PCR expression analysis for renal vitamin D receptor shows that the anti-BSP mAb therapy seems to bring about an up-regulation of the vitamin D receptor compared to placebo-treated 5/6 Nx rats and sham (see FIG. 4). The wet chemical analysis of the renal calcium phosphorus product produced no significant differences.

Heart and Aorta

The histological examination of the heart showed a significantly reduced interstitial fibrosis for 516 Nx rats (FIG. 6) receiving an anti-BSP IDK1 mAb therapy. The therapy also reduced cardiac perivascular fibrosis significantly (see FIG. 7). The results were significant compared to placebo-treated controls and sham (*p<0.0001; *p<0.05). The analyses for proteins indicated again that the described therapy may lead to a reduced cardiac expression of the matrix protein collagen III and of TGFβ-1, usually associated with fibrotic processes, compared to placebo-treated 5/6 Nx controls and sham.

While the total aortic calcification (FIG. 8) did not differ significantly in the aortas the wet chemical analyses showed a significantly reduced amount of phosphorous deposits. The RT-PCR analyses further support a reduced expression of the metalloprotease MMP9 (FIG. 9) compared to placebo-treated 5/6 Nx rats.

Thus, the results support that an administration of an antibody binding to a non-precipitated or soluble form of bone sialoprotein in plasma has a significant effect on tissue and vascular calcification in the chosen animal model for CKD. In summary: Von Kossa staining of aorta sections showed that extensive aortic calcifications were present in calcitriol-treated uremic rats. In contrast, no calcifications were observed in sham animals and the anti-BSP antibody treatment was able to decrease calcification. Anti-BSP-antibody treated animals also had a significantly decreased media-to-lumen ratio of intrarenal vessels and less perivascular fibrosis of intrarenal vessels. These results are very promising and give reason to believe in the possibility to use the anti-BSP-antibody to prevent vascular and arterial calcification in patients with CKD or ESRD.

The results for BSP elimination by an anti-BSP-antibody in the conducted experiment showed also impressive antifibrotic effects in the kidney and the heart. However, it is not clear, whether the observed antifibrotic effects are due to a reduced calcification, or whether the antibody has antifibrotic activity. Thus, it is contemplated to investigate the antifibrotic properties of the anti-BSP-antibody in an animal model of diabetic kidney disease, with fibrosis being one of the main characteristics of the chosen model. For this, we contemplate using another different rat model of vascular calcification in order to confirm the beneficial effects of anti-BSP-antibody under different circumstances.

Example 3 Antibodies Binding to BSP in Plasma

BSP is bound in plasma by complement factor H with high affinity. There have been produced antibodies against peptide partial structures of BSP (Fisher, L. W. et al., Acta Orthop Scand Suppl., 1995, 266, 61-655), against recombinant BSP (Stubbs J T 3rd et al. J. Bone Miner. Res. 1997 12(8), 1210-22), and against BSP isolated from bones, which antibodies failed to bind any BSP in plasma or serum. As the larger factor H molecule of 150 kDa seems to mask the smaller BSP of ca. 65 kDa (Fedarko N S et al., J. Biol. Chem., 200, 275, 16666-16672; WO 00/062065) we screened for an antibody which cross-reacts with BSP (rat or human) in serum or plasma, or a BSP fragment thereof, and this even in the presence of factor H or endogenous BSP receptors.

For this purpose we used conserved peptide epitopes from the human BSP sequence, more precisely, from human BSP II disclosed at UniProtKB/SWISS-PROT:P21815 (SIAL_HUMAN) and its natural variants at positions 195, 213, 219, 256, 268 and 270. As the human BSP further is a phosphorylated glycoprotein with phosphorylated serine at positions 31, 67, 74, 75. 94. 100, 149, 280; sulphated tyrosine and multiple complex glycosylation, we were looking specifically for potential peptide epitopes. Moreover, we prepared a multiplicity of rat monoclonal antibodies against BSP epitopes common in rat and human, coupled to a carrier, and tested the rat mAbs for binding to human BSP in plasma. For increasing the antigenicity we further used synthetically coupled BSP epitopes as described in EP1888631 B1 as well as BSP epitopes coupled with beta-alanine. Preferred artificial BSP epitopes for immunization and screening of the antibody libraries are indicated below:

SEQ ID NO: 1 YTGLAAIQLPKKAGDZ wherein Z represents one or more beta-alanine.

SEQ ID NO: 2 SENGEPRGDNYRAYEDEYSYFKGQGYDGYDGQNYYHHQZ wherein Z represents one or more beta-alanine.

SEQ ID NO: 3 ZEDATPGTQYTGLAAIQLPKKAGZSGGGGSAZGAKKPLQIAALGTYGTGP TADEZ wherein Z represents one or more beta-alanines. The peptide of SEQ ID NO: 3 has been derived from a human BSP wherein multiple accessible BSP epitope have been coupled using a spacer sequence such as SGGGGS.

We screened differentially a synthetic human antibody library for an antibody reacting with synthetic peptide epitopes derived and common to rat or human BSP which we assumed being accessible in plasma. Moreover, we screened a proprietary synthetic human antibody library (mAB-Factory GmbH, Braunschweig, DE), prepared in accordance with DE 4122599 C2 and WO 93/01288 (PCT/EP92/01524), for phagemid-expressed single chain antibodies binding to BSP peptide epitopes with a soluble peptide antigen as indicated and with human BSP in plasma. A respective full human antibody (AF165R4.2-E2) specific for human BSP in plasma was obtained and reconstructed.

Further, we isolated and sequenced a rat monoclonal antibody (anti-BSP_IDK1), and a partial proprietary humanized antibody library comprising humanized variants of the rat complementary determining region which binds to human BSP in plasma with high affinity. Moreover, a chimeric CDR-grafted human monoclonal antibody was obtained.

As there are no hard and fast rules for choosing the human acceptor frameworks into which to graft the donor CDRs, we disclose herein below the sequences of our fully human anti-hBSP antibody which binds to human BSP in plasma as well as of the CDR grafted chimeric antibody and the humanized monoclonal antibody which CDRs are based on the CDR of the rat monoclonal antibody (anti-BSP IDK1):

Heavy Chain (AF 165R4.2-E2) SEQ ID NO: 4

The underlined portion stands for the signal peptide (with an intron removed) and the portion in bold (underdotted) comprises the CDR.

Light Chain (lambda) SEQ ID NO: 5

The underlined portion represents the signal peptide. An intron has been removed for the translation in the signal peptide of the heavy chain. The portion in bold is the constant CH1-hinge-CH2-CH3 region of the antibody.

Moreover, a human chimeric version of a monoclonal rat antibody binding to a soluble form of BSP in plasma was produced.

chimeric version of a rat mAB (heavy chain) - IDK 1 SEQ ID NO: 6

Light Chain (kappa) SEQ ID NO: 7

The underlined portion represents the signal peptide. The portion in bold represents the constant CH1-hinge-CH2-CH3 region of the antibody.

Humanized mAB of IDK 1 (AF 177.3) - heavy chain SEQ ID NO: 8

Light Chain (kappa) SEQ ID NO: 9

The peptides used for screening the monoclonal rat antibodies for binding to human BSP in plasma were modified with beta-alanine for increasing affinity or peptides with multiple copies of a BSP epitope were used. In this way, we also found a human monoclonal antibody in our proprietary human antibody phagemid library which was then made fully human using recombinant technology (Stefan Dübel, edt., Handbook of Therapeutic Antibodies, Wiley-VCH 2010; ISBN 978-5-527-32902-1). Titration and competition experiments show that the monoclonal antibodies (anti-BSPJDK1 as well as chimeric version thereof, anti-BSP_IDK2 human mAb (clone AF165R4.2-E2) and the humanized antibody anti-BSP_IDK3 (clone AF177.3) bind close by if not the same epitope on human BSP in plasma while the rat mAb (anti-BSP IDK1) has highest affinity.

Example 4—BSP Plasmapheresis Material

There is any clinical evidence that an elimination of circulating BSP via plasmapheresis may cause osteoporosis or a bone disease. In this connection we note that postmenopausal woman suffering from osteoporosis even show elevated levels of serum BSP compared to perimenopausal healthy controls. Moreover, treatment with alendronic Acid® (INN) as well as hormone replacement therapy, which are established therapeutic treatment of osteoporosis, all lead to a reduction of serum BSP levels in postmenopausal women. Thus, there are good reasons to assume that an elimination of BSP from serum or plasma by plasmapheresis can become an accepted therapy for patients suffering from CKD or ESRD.

Moreover, we can relying on proven apheresis materials as there are established processes for the elimination of LDL-cholesterol, lipoprotein and/or apolipoprotein from human plasma. Suitable stationary immunosorbent materials are commercially available, e.g. GLOBAFFIN® and Immunosorba® (Fresenius Medical Care AG, DE). In brief, the therapeutic method for removal of the circulating BSP would require that the blood of the patient is first separated into blood cells and blood plasma using a machine. In a further step the plasma containing the BSP is passed extracorporally through one of more immunosorbent columns. The columns contain the monoclonal antibody against circulating BSP. Whilst the first column is loaded with BSP the second is rinsed (regenerated), to become available again for a further loading cycle. After removal of the circulating BSP, the plasma is mixed again with the blood cells and returned to the patient. Such an extracorporeal treatment of the blood usually takes between three and five hours and can be done using for example the Octo-Nova® machine (Diamed Medizintechnik GmbH, Köln, DE).

We contemplate testing this extracorporeal treatment in animal studies by obtaining a reduction of vascular calcification in adenine-induced nephropathy and a reduction of vascular calcification in diabetic nephropathy, using rats and Zucker diabetic fatty rat. Moreover, a novel companion test is being developed using the antibodies of example 3 to screen for BSP and anti-BSP-antibodies in animal and human blood. As mentioned, the immunosorbent material for a plasmapheresis will be used in the Octo-Nova apheresis system (Diamed Medizintechnik GmbH, Germany). In a later step, we intend to demonstrate that plasma BSP levels are related to mortality in patients with CKD or ESRD. The efficacy and biocompatibility (safety) of the BSP adsorbent material will be proven in art ex vivo study, and finally a tolerability apheresis study phase will be conducted to prove human safety, and reduction of BSP following apheresis in CKD patients. The test antibody (anti-BSP IDK2) was coupled to the stationary phase (Sephadex®) using the NHS method which proved more effective than coupling by BrCN. The coupling was done using a solution of the antibody at 1 mg/ml at 4 degrees Celsius with an NHS-activated column material in borate buffer (BBS, pH 10.0). The coupling efficiency of 78% was determined via the amount of antibody not coupled to the solid phase using the Bradford method. When an antibody concentration of 2 mg/ml was used, the coupling efficiency was 43% which corresponds to 0.86 mg mAb/ml Sephadex®. Thus, an increase of the antibody concentration did not lead to a substantially increased amount of mAb on the stationary phase. When using NHS-activated agarose as stationary phase we obtained a coupling efficiency of 77% in a solution comprising 1 mg/ml mAb and of 62% in a mAb solution comprising 2 mg/ml mAb. Thus, more mAb could be coupled onto agarose than on Sephadex® which can be explained that mAb was also coupled in the interior of the stationary phase.

Further parameters of the packed column were fluid flow through in relation to fluid pressure as well as the adsorption kinetics of BSP in relation to temperature and concentration (see FIGS. 10 and 11). For a maximum of BSP binding a temperature of 10 degrees was optimal while the binding kinetics were much better at 30 degrees, allowing shorter application times.

The BSP material could be desorbed again from our test columns using a mixture of citrate and vitamin C at a pH of 2.8 to 4. The binding capacity and kinetics only decreased from 85% to 73% in the course of eight rounds of apheresis which is acceptable for these initial tests. The binding kinetics proved equally acceptable (see FIG. 12)

In summary, the optimal parameters for an immunosorbent column material is beaded cross-linked NHS-activated agarose as this gives a reusable and safe column material. The coupling is preferably done in an alkaline carbonate or borate buffer at 4 to 8 degrees Celsius. The binding temperature was optimal at 30 degrees Celsius and about 75 ml blood could be purified from BSP using 15 ml column material. 

What is claimed is:
 1. A medicament for treating extracellular tissue and vascular calcification, atherosclerosis, arteriosclerosis, and arterial calcification comprising an effective amount of a receptor molecule specifically binding to human bone-sialoprotein (BSP) in blood, plasma or serum.
 2. The medicament as claimed in claim 1, wherein the receptor molecule is a human monoclonal antibody or a humanized monoclonal antibody or a rat monoclonal antibody4.
 3. The medicament as claimed in claim 2, wherein the antibody comprises one or more functional portions of a protein sequence as disclosed in any of SEQ ID NO: 4, 5, 6, 7, 8 and
 9. 4. The medicament as claimed in claim 2, wherein the receptor molecule or antibody comprises one or more of the functional complement determining regions (CDR) contained in any protein sequence of SED ID NO: 4, 5, 6, 7, 8 and
 9. 5. A medicament for treating extracellular tissue and vascular calcification as claimed in claim 1, wherein the receptor molecule recognizes an antigen determinant or epitope of BSP which is accessible in plasma and bound by an antibody having any protein sequence of SEQ ID NO: 4, 5, 6, 7, 8 and
 9. 6. A receptor molecule or antibody as described in claim 2, which is bound to or contained in any solid phase material selected from beads, agarose, material used for apheresis, material used for plasmapheresis, microtiter plate, vessel wall.
 7. The receptor molecule or antibody of claim 2 which is comprised in diagnostic system or kit, preferably a kit for companion diagnostic of renal replacement therapy, dialysis, CKD, ESRD, tissue and vascular calcification, atherosclerosis, arteriosclerosis, arterial calcification.
 8. An extracorporeal blood treatment system comprising: means for withdrawing blood from a patient; means for separating blood cells and plasma; means for transporting the plasma through a trap for soluble BSP, the BSP trap including a substrate having an immobilized species, the species being adapted to reduce the soluble BSP concentration in the blood to a concentration that prevents vascular and tissue calcification, thereby producing BSP-depleted plasma; and means for returning treated plasma and blood cells back to the patient.
 9. The extracorporeal blood treatment system of claim 8, further comprising: means for transporting the blood and/or plasma through a calcium trap, the calcium trap including a substrate having an immobilized species, the species being adapted to reduce the calcium concentration in the blood to a concentration that prevents formation of a precipitate of calcium and BSP in the extracorporeal blood treatment system, thereby producing calcium-depleted blood; means for treating the calcium-depleted blood or plasma downstream of the calcium trap by an extracorporeal plasma treatment device, which may also comprise a trap for bone sialoprotein; and means for infusing calcium into the treated calcium-depleted blood downstream of the extracorporeal blood treatment device to add calcium to the treated calcium-depleted blood.
 10. A method for plasmapheresis comprising the use of a trap for soluble BSP.
 11. A method of reducing vascular and soft tissue calcification comprising a plasmapheresis intervention whereby excess BSP is eliminated from the circulation.
 12. The method of claim 11, whereby excess is eliminated from the circulation in a hemodialysis process.
 13. A method of reducing arterial and vascular calcification comprising the use of therapeutic antibodies against BSP.
 14. The method of claim 11, whereby the overall outcome of renally impaired patients with CKD or ESRD is improved. 